The present invention is directed to an expansion bolt assembly for use in boreholes having an annular undercut section near the base of the borehole. The assembly includes a plurality of annular segments in a ring-shaped arrangement which can be displaced radailly outwardly into the undercut section. An expansion sleeve is driven into the borehole and displaces the annular segments radially outwardly into the undercut section. An anchor bolt extends into the borehole and has a head at its end inserted first into the borehole whereby the head presses against the annular segments in the axial direction of the borehole for supporting the segments within the undercut section.
In a known expansion bolt assembly annular segments are displaced radially by an expansion sleeve and pressed into an undercut section of a borehole for effecting an anchorage. The expansion sleeve is displaced into the borehole until the annular segments abut against the radial base of the undercut section. Accordingly, the radial displacement of the annular segments and the axial displacement of the expansion sleeve is dependent on the radial depth of the undercut section. Such an expansion bolt assembly has considerable disadvantages including the possibility of insufficient absorption of transverse forces as well as a complicated structure. The complicated structure involves the annular segments fabricated as individual parts and retained in the expansion bolt assembly by an annular spring. To maintain uniform spacing between the annular segments, they are provided with leg-like projections extending into slot-like recesses.